Speaker

Presentation Abstract

We electrofished for juvenile Chinook presence in 63 small coastal streams draining into Whidbey basin. The streams sampled range in watershed size from 3 to 1,862 hectares with channel slopes ranging from less than 1% to 38% for electrofished reaches. Bankfull channel width of electrofished stream reaches range from 0.8 to 6.9 meters. In 32 of the 63 streams we found juvenile Chinook salmon present on at least one of the sampling days over the six year study period (2008 – 2013. Most juvenile Chinook salmon were caught in the months of January through May each year. Juvenile Chinook body size found in the small streams was similar to or larger than juvenile Chinook body size found in adjacent nearshore habitat from January through April. After April, juvenile Chinook salmon were larger in nearshore areas than in small streams. While in small streams, individual juvenile Chinook reared an average of 38.5 days and grew 0.23 mm/day. Statistical analysis suggests four factors influence whether juvenile Chinook salmon are present within Whidbey Basin small streams: 1) distance to nearest Chinook salmon bearing river, 2) stream channel slope, 3) watershed area, and 4) presence and condition of culverts at the mouth of stream. Streams further from Chinook salmon bearing rivers and with steeper channel slopes had lower juvenile Chinook salmon presence rates. A minimum watershed size of 45 hectares with channel slopes less than 6.5% may be necessary for juvenile Chinook salmon potential. Culverts at stream mouths likely cause upstream migration problems for small fish such as Chinook salmon fry. Streams of this size are often not considered salmon habitat because many flow seasonally and do not provide habitat for spawning salmon. However, we found that numerous small streams entering the Whidbey Basin do provide rearing habitat for fry migrant Chinook salmon originating from the three nearby rivers (Skagit, Snohomish, and Stillaguamish). These small streams are not well mapped and may be subject to inadequate protection as fish habitat. Better mapping of small streams and a predictive model for juvenile Chinook salmon potential would help managers better protect this unique habitat type.

Session Title

Session S-04C: Importance of Puget Sound Lowland Streams

Conference Track

Freshwater

Conference Name

Salish Sea Ecosystem Conference (2014 : Seattle, Wash.)

Document Type

Event

Start Date

1-5-2014 8:30 AM

End Date

1-5-2014 10:00 AM

Location

Room 606

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Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.

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Language

English

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May 1st, 8:30 AMMay 1st, 10:00 AM

Juvenile Chinook Salmon Rearing in Small Non-natal Streams Draining into the Whidbey Basin

Room 606

We electrofished for juvenile Chinook presence in 63 small coastal streams draining into Whidbey basin. The streams sampled range in watershed size from 3 to 1,862 hectares with channel slopes ranging from less than 1% to 38% for electrofished reaches. Bankfull channel width of electrofished stream reaches range from 0.8 to 6.9 meters. In 32 of the 63 streams we found juvenile Chinook salmon present on at least one of the sampling days over the six year study period (2008 – 2013. Most juvenile Chinook salmon were caught in the months of January through May each year. Juvenile Chinook body size found in the small streams was similar to or larger than juvenile Chinook body size found in adjacent nearshore habitat from January through April. After April, juvenile Chinook salmon were larger in nearshore areas than in small streams. While in small streams, individual juvenile Chinook reared an average of 38.5 days and grew 0.23 mm/day. Statistical analysis suggests four factors influence whether juvenile Chinook salmon are present within Whidbey Basin small streams: 1) distance to nearest Chinook salmon bearing river, 2) stream channel slope, 3) watershed area, and 4) presence and condition of culverts at the mouth of stream. Streams further from Chinook salmon bearing rivers and with steeper channel slopes had lower juvenile Chinook salmon presence rates. A minimum watershed size of 45 hectares with channel slopes less than 6.5% may be necessary for juvenile Chinook salmon potential. Culverts at stream mouths likely cause upstream migration problems for small fish such as Chinook salmon fry. Streams of this size are often not considered salmon habitat because many flow seasonally and do not provide habitat for spawning salmon. However, we found that numerous small streams entering the Whidbey Basin do provide rearing habitat for fry migrant Chinook salmon originating from the three nearby rivers (Skagit, Snohomish, and Stillaguamish). These small streams are not well mapped and may be subject to inadequate protection as fish habitat. Better mapping of small streams and a predictive model for juvenile Chinook salmon potential would help managers better protect this unique habitat type.